Daily rhythms after vaccination on specific and non-specific responses in Nile tilapia (Oreochromis niloticus)

ABSTRACT

We evaluated the daily changes in immunological and hematological factors in tilapia (Oreochromis niloticus) after an immunization period with a subsequent challenge. Experiments were divided into two phases: Phase 1 (immunization): 144 fish were distributed into two groups with 72 fish in six tanks. One group (T1) was immunized, comprising six vaccination time points (ZT schedule = ZT2 h, ZT6 h, ZT10 h, ZT14 h, ZT18 h, ZT22 h). The same schedule was applied to the other group, but with saline solution (non-vaccinated: T2). Both groups remained in the laboratory for 30 days (considered the immunization period). Phase 2 (challenge): on day 30, both vaccinated and non-vaccinated groups were challenged with Streptococcus agalactiae (2.0 × 10⁷ CFU mL⁻¹) following the same ZT schedule to stimulate the immune response without leading to widespread infection and mortality. On day 45, blood and head kidney samples were collected during the same ZT schedule. The variations in time of the following parameters within each group were evaluated: hematology, peroxidase activity, IgM, tnf-α3, tgf-β1, il-1β and il-12 gene expression. No significant mortality was observed for the groups or the ZT schedule (p > 0.05). Daily rhythms with diurnal acrophases were found in T2 for il12, tnf-α3 and tgf-β1 expression gene, while the acrophases of the peroxidase level, hematocrit and thrombocytes were at nighttime (p < 0.05). In contrast, most of the parameters in the vaccinated tilapia showed no daily rhythms (p > 0.05), except IgM. For all the parameters, the interaction effect between time and treatment (vaccinated and non-vaccinated groups) depended on ZT. Our results reveal that the humoral and non-specific immune system displayed a circadian rhythm based on the light-dark cycle, which could be affected by the vaccination procedure in tilapia.

KEYWORDS:

• Biological rhythms
• endogenous clock
• freshwater fish
• gene expression
• rhythmic immune network

Acknowledgements

The authors thank Aquavale for supplying juvenile tilapia; Dr. Veridiana Fernandes da Silveira to help in blood analysis and Dr. Carlos Eduardo Crispim de Oliveira Ramos to help in the statistical analysis.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

This work was supported by the grant in aid from the Programa Nacional de Desenvolvimento Científico e Tecnológico, projeto Universal/CNPq, Special Visiting Researcher Project-PVE, CNPq (401416/2014-3) to R. Fortes-Silva and F.J. Sánchez-Vázquez. R. Fortes-Silva was funded through a research fellowship from CNPq/Brazil (Produtividade em Pesquisa-PQ) and J.F. López-Olmeda was funded through a research fellowship granted by the Spanish Ministry of Economy and Competitiveness (Juan de la Cierva Program).